Compensation of neural delays in visual-motor behaviour: No evidence for shorter afferent delays for visual motion

There are significant neural transmission and processing delays within the nervous system. How then are behaviours observed both in nature and high-speed ball games, which require temporal accuracy to within several milliseconds, possible? Until recently, most investigators attributed the observed success in interceptive behaviours to learning or prediction built into motor programs that take these delays into account. Several investigators have proposed, however, that sensory mechanisms also contribute to compensation. Sensory compensation is particularly important when moving objects are the targets of interceptive behaviour, as in this case neural delays in the visual system could lead to errors in the communication of crucial position information of the object of interest. However, given the biological significance of visual motion the visual system could have evolved neural pathways optimized for the rapid transmission of motion signals. Alternatively, the visual system could take a sample of visual motion and compensate for the delays through prediction based on the sample. This mechanism is the visual analogue of the previously proposed "internal forward model" for motor control. We conducted four experiments using the flash-lag effect to ask if the nervous system is naturally geared to processing moving items with a speed greater than stationary flashes. Our results show that the nervous system does not process moving items more quickly than stationary flashes.